I.Further purification of the FOK rat strainFOK rats had been selected by heat resistance and sibmated up to 40th generation in total. On the other hand, FOK rats were born by caesarean section into disinfected vinylene-isolator. They were gave milk by SPF foster mother. It was demonstrated by quarantine that pups had no specific pathogens. Thus, it became possible to keep FOK rat as a SPF animal and send it safely to other institute.II.The effects of hyperthermiaDuring hyperthermia higher than 40ﾟC,common rats salivate. FOK rats secreted saliva for 300 min in spite of severe dehydration, although other rats secreted small amount of saliva only for 30-120min. On the other hand, at 33ﾟC body temperature in FOK rat was lower than those in other rat strains, although these rats did not salivate in response to heat. Thermogenesis in brown adipocyte in FOK rat was lower during hyperthermia in vitro than those in other rat strains. These findings suggested possible mechanism contributing to diminish body temperature rising in FOK rat besides thermal salivation. Dark neurons were found in ischemic areas and other areas distant from ischemic areas.III.Congenital changes in consequence of genetic resistance adaptation to heatAt 24ﾟC body temperature in FOK rat was lower than those in other rat strains. Submandibular salivary glands in FOK rat were enlarged. FOK rat was also cold resistant rat.